The present invention involves an improved chopper for chopping continuous or very long loose items such as fiber, fiber strands, yarn, wire, string, ribbon, tape and the like by pulling the item(s) into the chopper while the loose items are held tightly against the surface of a rotating backup roll with a rotating idler roll biased against the backup roll and carrying the item(s) on into a nip between a rotating blade roll and the rotating backup roll where they are separated into short pieces. More specifically the present invention involves a chopper having an improved mounting for an idler roll which allows the idler roll to reliably self align with the surface of a back up roll to more reliably and more effectively hold down and pull item(s) being pulled and chopped such as loose wet or dry strands of glass fibers with, or without, a chemical sizing thereon.
It has long been known to chop continuous fibers or fiber strands into short lengths of about 3 inches or shorter. Billions of pounds of such product including chopped glass fibers and fiber strands are produced each year in process and chopping apparatus such as disclosed in U.S. Pat. Nos. 5,970,837, 4,398,934, 3,508,461, and 3,869,268, the disclosures of which are incorporated herein by reference. The choppers disclosed in these patents comprise a blade roll containing a plurality of spaced apart blades for separating the fibers into short lengths, a backup roll, usually driven, which the blades work against to effect the separation and which pulls the fibers or fiber strands and an idler roll to hold the fibers or fiber strands down onto the surface of the backup roll. In the chopped fiber processes disclosed in these patents, the chopper is usually the most productivity limiting equipment in the processes which are 365xc3x9724 type processes, i.e. operate continuously every day of the year, 24 hours each day. Therefore, improvements in the chopper which allow the chopper to pull and chop faster, for longer times between maintenance shutdowns, and/or to pull and chop more fibers or fiber strands at a time have an extremely positive impact on productivity and production costs.
In the published prior art the idler roll has been mounted and held against the surface of the back up roll in a generally rigid manner and with a variable force such as a force applied by an air or hydraulic cylinder. The working surface of the idler roll has been knurled and chrome plated in the past to better grip the fibers or fiber strands to prevent the fibers or fiber strands from sticking to the roll and wrapping and to avoid having to shut the chopper down to remove the wrap. Normally several strands such as up to 14 are fed into the chopper, each strand containing 2000 or more fibers. As more fiber strands and fibers are fed into the chopper it becomes more difficult to pull all of the strands and fibers at the same speed, so more pressure is applied to the cylinder pushing the idler roll against the backup roll with more force. If all of the strands or fibers are not pulled at the same speed, the slower strands and fibers will have a greater fiber diameter which is unacceptable and the bushings of the slower strands frequently will not operate at the proper temperature causing more frequent breakouts and/or additional fiber diameter variations, both of which are unacceptable. Also, fiber slippage can cause some of the fibers to be cut to shorter lengths than desired resulting in an unacceptable product.
As the pulling speed is increased, and/or as the number of strands and fibers are increased, above about 3000-4000 ft./min. (FPM), depending on the product, the present state of the art choppers begin to vibrate and the idler roll begins to allow one or more of the strands to slip some thus reducing the pulling speed of one or more of the strands. Also, if all of the strands are not pressed between the idler roll and the elastomer layer of the backup roll, a strand can slip partially out of the nip leaving some of the fibers unchopped, producing double cuts and stringers in the chopped product and causing the product to be scrapped. This condition worsens as the backup roll and blades become worn with use, typically about 6-24 hours following a chopper rebuild in which the blade roll is replaced with a roll having new blades and the backup roll is replaced with either a refurbished or new backup roll. The backup roll has a working layer of polyurethane at least about a half inch thick on the surface of a metal wheel. As the chopper life increases the surface of the backup roll becomes chopped up due to the blades pressing and cutting into the polyurethane.
Periodically the backup roll must be removed and either the polyurethane layer turned down on a lathe or sander or must be replaced with a new layer of polyurethane. It would be very desirable to be able to run the chopper at higher speed without vibration and strand slippage to make good chopped fiber than is possible with the current state of the art choppers because the remainder of the process is capable of producing fiber that can be pulled much faster in terms of speed and pounds of fiber per hour than is currently possible. Also, in the preferred state of the art chopper the idler roll mount is exposed to broken fiber and sizing being thrown from the various rolls on the chopper and must be frequently cleaned to avoid serious malfunction at current speeds.
It has been discovered that the reason for certain strands slipping on the idler/backup roll of the current choppers is the manner in which the idler roll is mounted, the manner in which the force is applied to hold the idler roll onto the surface of the backup roll and the fact that the peripheral surface of a new and used backup rolls often have a slight taper from side-to-side or misalignment with the idler roll, either initially or after the new backup roll has been in use for a few hours.
The present invention is a chopper having an improved idler roll mount assembly for a chopper for separating long lengths of one or more unwound items selected from a group consisting of fibers, fiber strands, wires, strings, tape(s), strip(s) and ribbon(s) into short lengths while one or more of, preferably a plurality of, the long lengths of material are pulled into the chopper in an unwound form at speeds exceeding 1,000 FPM, preferably at speeds exceeding 2000 FPM by a rotating idler roll pressing the item(s) against the peripheral surface of an elastomer layer on the peripheral surface of a rotating backup roll which carries the item(s) on into a nip between the elastomer layer and a rotating blade roll. The item(s) being chopped can be either dry or wet with or without a chemical sizing on the surface of the item(s). The chopper having an improved idler roll mount assembly comprises a blade roll having a plurality of spaced apart blades in its peripheral surface, a backup roll having an elastomeric working layer on its periphery, and an idler roll, preferably having a knurled surface.
The improvement comprises a mount assembly for the idler roll having a yoke spaced from the peripheral surface of the idler roll that spans the length of the idler roll and beyond, each end of which turns down to support an axle about which the idler roll is free to rotate, a connector connecting said yoke to a shaft whose axis is perpendicular to an axis of said connector, said connector allowing said yoke to rotate back and forth around the axis of said connector, said shaft being held in a rotatable manner by a structural member of the chopper in such a manner that the outer peripheral surface of the idler roll is or can be in contact with, preferably with the full width of, the outer peripheral surface of the backup roll and/or item(s) on the outer peripheral surface to be chopped, an arm rigidly connected to said shaft, a source of a variable force for said arm or a means for applying a variable force to said arm, which force causes the outer peripheral surface of said idler roll to press against either the peripheral surface of said backup roll or against one or more of said items laying on the peripheral surface of said backup roll and thus holding the peripheral surface of said idler roll into pulling contact with said one or more of said items. Preferably, the chopper has an enclosed cabinet on the inboard side of the outboard face of the front plate and preferably at least some of the components of the idler roll mount are located in this cabinet to protect them from foreign matter in the environment around the idler roll. This foreign matter includes water mist, chemical sizing from the surface of fibers, dust and pieces of the item(s) being chopped.
The connector can either be a female socket or a male stub rigidly or rotatably attached to the shaft or to the yoke and the male stub is attached to either the yoke or to the shaft in either a rigid or rotatable manner. The preferred means for applying a force to the arm is either an air or hydraulic cylinder, most preferably an air cylinder, but can be other sources of force such as a high torque motor mounted to the structure of said chopper, the rotor of said motor eccentrically attached to said arm. The arm could be dispensed with by attaching the end of the shaft opposite the end portion attached to the connector to a rotor of a high torque motor, the latter being mounted appropriately to a frame member of the chopper.
Optional items on the present invention include an air purge system for applying positive fluid pressure to the interior of the yoke pivoting mechanism, including the connector, to prevent foreign matter like water, chemical sizing and fiber or fiber chips from entering and impeding the free pivoting action. The fluid is preferably air but could be other gases and liquids such as water. Also, the air purge system can include a fluid cooling system for the idler roll bearing(s) as well as positive fluid pressure in the interior of the idler roll, again to prevent intrusion by foreign material present in the vicinity of the idler roll during operation and cleaning. Other optional features include means for limiting the degree of rotation of the idler roll yoke or axis as an aid to a mechanic when changing a backup roll and locator means to aid the mechanic, etc. in replacing an idler roll or idler roll mount sub-assembly. Also, various known means for applying a force to press the idler roll into the item(s) being chopped and towards the surface of the elastomer layer can be used.
The invention also includes a method of chopping items as described above using an improved chopper containing an improved idler roll mount as described above to permit a higher productivity of chopped fiber than is obtained with prior art choppers while also enjoying an idler roll mount that does not require frequent cleaning to avoid malfunctions and/or scrap caused by an exposed idler roll mount and force actuator.
When the word xe2x80x9caboutxe2x80x9d is used herein it is meant that the amount or condition it modifies can vary some beyond that so long as the advantages of the invention are realized. Practically, there is rarely the time or resources available to very precisely determine the limits of all the parameters of one""s invention because to do so would require an effort far greater than can be justified at the time the invention is being developed to a commercial reality. The skilled artisan understands this and expects that the disclosed results of the invention might extend, at least somewhat, beyond one or more of the limits disclosed. Later, having the benefit of the inventors disclosure and understanding the inventive concept and embodiments disclosed including the best mode known to the inventor, the inventor and others can, without inventive effort, explore beyond the limits disclosed to determine if the invention is realized beyond those limits and, when embodiments are found to be without unexpected characteristics, those embodiments are within the meaning of the term about as used herein. It is not difficult for the skilled artisan or others to determine whether such an embodiment is either as might be expected or, because of either a break in the continuity of results or one or more features that are significantly better than reported by the inventor, is surprising and thus an unobvious teaching leading to a further advance in the art.